Cantilever skidding system on a drilling rig

ABSTRACT

The present invention provides an improved cantilever ( 10 ) for skidding on a platform ( 30 ) of a drilling rig. The cantilever ( 10 ) has two longitudinal members ( 12 ) while an edge ( 32 ) of the platform ( 30 ) has two transverse members ( 14,14   a ). The longitudinal and transverse members are connected at each interposition by a sliding and swivel assembly ( 20, 20   a, . . .    20   d ). Each sliding/swivel assembly ( 20, 20   a . . .    20   d ) is connected by an actuator ( 24, 24   a ) to the longitudinal or transverse member so that the cantilever ( 10 ) is operable to be displaced on the platform ( 30 ) by translation, rotation or a combination of translation and rotation.

FIELD OF INVENTION

The present invention relates to an improved cantilever skidding systemon a platform of a drilling rig. In particular, the invention relates toa system for extending a drill-floor beyond a rectangular area that isconventionally accessible with two orthogonal axes of motion.

BACKGROUND

A typical offshore drilling rig has a platform supported on legs and acantilever mounted on the platform. Mounted on a drill operation end ofthe cantilever is a drill floor. The cantilever is moveable in alongitudinal direction of the cantilever such that the drill operationend of the cantilever extends beyond the platform, whilst the drillfloor is moveable on the cantilever in a direction transverse to thelongitudinal direction. As a result, the drill point can only be locatedwithin a rectangular area described by the longitudinal and transverseaxes of the cantilever and the drill floor.

The transverse distance covered by the drill floor is limited by thewidth of the cantilever, which is determined by the distance betweencantilever beams extending in the longitudinal direction. To obtain areasonably wide drilling pattern, the cantilever must also be reasonablywide. Another limitation of the conventional cantilever is that thedrill floor creates an asymmetric load on the longitudinal cantileverbeams, for example, when the drill floor is moved to a maximal distancein the transverse direction and the longitudinal cantilever beam on theside to which this movement takes place is subjected to a heavier loadthan the other longitudinal cantilever beam. As a result, eachlongitudinal cantilever beam must be sturdy and heavily constructed.

Attempts have been made to overcome some of these limitations. Forexample, U.S. Pat. No. 6,171,027 assigned to Marine StructureConsultants discloses a drill floor that is fixedly mounted on thecantilever so that the load on the longitudinal cantilever beams iscentrally or symmetrically located whilst the beams for transversemotion are located on the platform. This design has the advantage thatthe longitudinal cantilever beams can be of a lighter construction andthe range of transverse motion is increased. However, the drillingpattern is still limited by the longitudinal and transverse motions ofthe cantilever.

U.S. Pat. No. 6,729,804 assigned to Itrec B.V. describes a drilling righaving a platform, a cantilever and a supporting cart disposed betweenthe cantilever and the platform. The supporting cart slides transverselyon the platform whilst the cantilever slides longitudinally on thesupporting cart on four friction reducing bearings. However, thedrilling pattern is still limited by the longitudinal and transversemotions of the cantilever.

U.S. Pat. No. 7,083,004 also assigned to Itrec B.V. describes a drillingrig having a platform, a cantilever and a supporting cart disposedbetween the cantilever and the platform. The supporting cart pivotsabout a pivot point on the platform whilst the cantilever slideslongitudinally on the supporting cart. The drilling pattern is now partsectorial over the edge of the platform as constrained between twoadjacent legs of the drilling rig. U.S. Patent '004 also describes acantilever with the pivot point being moveable in a direction transverseto the longitudinal direction to create an ellipsoidal drilling pattern.FIG. 1 shows the cantilever described in U.S. Patent '004.

WO 2007/043856 filed by Itrec B.V. describes a rig having a platform anda cantilever. The cantilever has longitudinal rails for extending thecantilever beyond the platform. WO 2007/043856 further discloses railextensions at the inner end of the longitudinal rails. The railextensions allow the longitudinal rails to be further extended so thatthe drilling area is increased.

It can thus be seen that there exists a need for another cantileverskidding system for an offshore platform that allows the drill floormounted on the cantilever to be moved over a large area and yetovercoming the limitations of the prior art systems, such as, theinconvenience in moving the curved rail 444 of U.S. Pat. No. 7,083,004.

SUMMARY

The following presents a simplified summary to provide a basicunderstanding of the present invention. This summary is not an extensiveoverview of the invention, and is not intended to identify key featuresof the invention. Rather, it is to present some of the inventiveconcepts of this invention in a generalised form as a prelude to thedetailed description that is to follow.

In one embodiment, the present invention provides a drilling rig. Therig comprises: a platform having a pair of substantially paralleltransverse members near an edge thereof; a cantilever mountable on theplatform, said cantilever having a pair of substantially longitudinalmembers along the length of the cantilever, said longitudinal membersare substantially orthogonal to the pair of transverse members; and asliding and swivel assembly connecting the longitudinal and transversemembers at each interposition of said longitudinal and transversemembers such that a sliding/swivel assembly is moveable relatively onthe relevant longitudinal or transverse member to translate and/orrotate the cantilever with respect to the platform.

In another embodiment, the present invention provides a method ofdisplacing a cantilever on a platform of a drilling rig. The methodcomprises: disposing said cantilever on said platform, with saidcantilever having two substantially parallel members along thecantilever's longitudinal dimension; disposing two substantiallyparallel transverse members near an edge of said platform;interconnecting said longitudinal and transverse members by a slidingand swivel assembly at each interposition; and connecting an actuatorbetween a sliding/swivel assembly and said longitudinal/transversemember, wherein said actuator is operable to translate and/or rotatesaid cantilever with respect to said platform.

In another embodiment of the present invention, the sliding and swivelassembly comprises an upper sliding block, a lower sliding block and aswivel member interconnecting the upper and lower sliding blocks, saidupper sliding block is connected to the longitudinal member whilst thelower sliding block is connected to the transverse member. Thesliding/swivel assembly also comprises shoulders, necks and annularsurfaces to withstand torsion, tension and compression loads, with eachpair of mating surfaces having a bearing plate therebetween.

In another embodiment of the present invention, a sliding/swivelassembly is connected by an actuator to the longitudinal member and/ortransverse member. In one embodiment, the actuator is a fluid actuator;in another embodiment, the actuator is a screw actuator. In a furtherembodiment, the actuators are connected in series; in another, theactuators are connected in parallel. In yet another embodiment of thepresent invention, a sliding/swivel assembly is connected by arack-pinion assembly to the longitudinal/transverse member.

In a further embodiment of the present invention, the pair of transversemembers are unequal in length, with the transverse member near the edgeof the platform being longer.

In yet a further embodiment of the present invention, rotation of thecantilever is created by counter-motions of the actuators orracks/pinions associated with the longitudinal members or transversemembers or both members.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be described by way of non-limiting embodiments ofthe present invention, with reference to the accompanying drawings, inwhich:

FIG. 1 illustrates a known skidding system described in U.S. Pat. No.7,083,004.

FIG. 2 illustrates a plan view of a cantilever system on a drilling rigin accordance with an embodiment of the present invention;

FIG. 3 illustrates a longitudinal section of the cantilever shown inFIG. 2 in accordance with another embodiment of the present invention;

FIG. 4 illustrates a transverse section of the cantilever shown in FIG.2 in accordance with another embodiment of the present invention;

FIG. 5A illustrates a sectional view of a swivel member in accordancewith another embodiment of the present invention; FIG. 5B illustrates asectional view of a swivel member in accordance with yet anotherembodiment;

FIG. 6A illustrates rotation of the cantilever about a fixed pivot,whilst FIG. 6B illustrates rotation of the cantilever by counter-motionsof the actuators in accordance with another embodiment of the presentinvention;

FIG. 7 illustrates a locus of a drilling point created by displacing thecantilever shown in FIG. 2; and

FIG. 8 illustrates rotation of the cantilever of the present inventionin a manner that is different from that of a prior art.

DETAILED DESCRIPTION

One or more specific and alternative embodiments of the presentinvention will now be described with reference to the attached drawings.It shall be apparent to one skilled in the art, however, that thisinvention may be practised without such specific details. Some of thedetails may not be described at length so as not to obscure theinvention. For ease of reference, common reference numerals or series ofnumerals will be used throughout the figures when referring to the sameor similar features common to the figures.

FIG. 2 shows a plan view of a cantilever 10 system on an offshoreplatform 30 according to one embodiment of the present invention. Asshown in FIG. 2, the cantilever 10 is operable to extend over an edge 32of the platform 30 in a longitudinal direction of the cantilever ordirection X. The platform 30 is supported by four jack-up legs 40. On adistal or operational end of the cantilever 10 is a drill floor 50,which has a drilling axis P extending perpendicular to both the drillfloor 50 and the cantilever 10, i.e. in direction Z with reference tothe coordinates shown in FIG. 2. Each cantilever 10 has a longitudinalbeam or member 12 on each of its two sides. Mounted along the edge 32 ofthe platform 30 is a transverse beam or member 14, which issubstantially orthogonal to the longitudinal members 12, i.e. transversemember 14 is aligned in the Y direction. Substantially parallel to thetransverse member 14 is another transverse member 14 a, the latter beingslightly shorter than the former. At each intersection of thelongitudinal member 12 and the transverse member 14,14 a, as seen in theplan view in FIG. 2, is a sliding and swivel assembly 20; altogether,there are four such sliding and swivel assemblies 20 a, 20 b . . . 20 d.In addition, to prevent the cantilever 10 from overturning, twohold-down claws 60 are provided on the cantilever, for example, at anend opposed to the operational end.

FIG. 3 shows a longitudinal sectional view of the cantilever 10. FIG. 4shows a transverse sectional view of the cantilever 10. As shown inFIGS. 3 and 4, each sliding and swivel assembly 20 a, 20 b . . . 20 dinter-connects a longitudinal member 12 with a transverse member 14,14a. Each sliding and swivel assembly 20 is made up of an upper slidingblock 21, a lower sliding block 22 and an interconnecting swivel member23. Each sliding/swivel assembly 20 is translated by a fluid actuator24,24 a relative to each of the longitudinal 12 and transverse 14,14 amembers. One end of each fluid actuator 24,24 a is connected by a pin toa connecting end 25 at the sliding/swivel assembly 20 whilst the other(second) end is connected by another pin to another connecting end 26 ata rail block 27 on the relevant longitudinal/transverse member. Eachlongitudinal/transverse member has a plurality of holes 29 that areequally spaced apart along the member. Each rail block 27 has a bore anda pivot pin 28 for connection with a hole 29 on the respectivelongitudinal 12 or transverse member 14,14 a. By shifting the pivot pin28 on the holes 29 along the associated member 12,14,14 a andextending/retracting each fluid actuator 24,24 a, the relevantsliding/swivel assembly 20 is relatively translated intermittently orstepwise on the member.

FIG. 5A shows a sectional view of a swivel member 23 according to anembodiment of the present invention. As shown in FIG. 5A, the swivelmember 23 has an upper flange 230 and a lower flange 240. An externalside of the upper flange 230 is connected to the upper sliding block 21,for example, by bolts and nuts, welding, and so on. Similarly, theexternal side of the lower flange 240 may be connected to the lowersliding block 22 by bolts and nuts, welding, and so on. An internal sideof the upper flange 230 has a two-steps neck 232 and an annular end orflange 238. The two-steps neck 232 defines an internal shoulder 234therebetween. An external side of the lower flange 240 is connected tothe lower sliding block 22 whilst the internal side has a neck 242 thatdefines a shoulder 244 and an annular flange 248. The internal side ofthe upper flange 230 engages with the internal side of the lower flange240 in a rotatory manner through bearing plates 250, 252, 254; that is,the shoulders 234, 244 of the upper and lower flanges 230,240 arerotatory connected by bearing plates 250; the necks 232, 242 arerotatory connected by bearing plates 252; and the annular flanges238,248 are rotatory connected by bearing plates 254. Theinterconnecting rotatory surfaces on the internal sides of the upper andlower flanges thus allow relative rotation of the upper flange 230 andlower flange 240, yet allowing each sliding/swivel assembly 23 towithstand tension and compression loads.

FIG. 5B shows a sectional view of a swivel member 23A according toanother embodiment of the present invention. As shown in FIG. 5B, theswivel member 23A is similar to the swivel member 23 except that swivelmember 23A does not have the annular flanges 238, 248. Accordingly, thebearing plate 254 is disposed between the shoulder 244 and a lowersurface of the upper flange 230.

In use, the fluid actuators 24,24 a are actuated to extend/retract orpush/pull the cantilever 10 in the longitudinal or X-direction, topush/pull the cantilever 10 in the transverse or Y-direction, to rotatethe cantilever 10 about the Z-axis, or any combinations of thesemovements. In one embodiment, the cantilever 10 has a pair of fluidactuators 24 associated with the longitudinal member 12 and a pair offluid actuators 24 a associated with the transverse member 14, 14 a. Inanother embodiment, the cantilever 10 has two pairs of fluid actuatorsassociated with each of the longitudinal and transverse members. In yetanother embodiment, the cantilever 10 has different numbers of fluidsactuators associated with the longitudinal and transverse members. Forexample, to translate the cantilever 10 in the X- or Y-direction, thepair(s) of fluid actuators 24, 24 a in the relevant direction is/aresynchronously actuated to translate the cantilever 10 in an intermittentor stepwise manner.

To rotate the cantilever, one or more fluid actuators associated with anadjacent or opposite sliding/swivel assembly or assemblies is/areactuated in cooperation to create a turning moment or torque to rotatethe cantilever in the desired direction. For example, FIGS. 6A and 6Bshow a cantilever 10 with four sliding/swivel assemblies 20 a . . . 20 dand a pair of longitudinal fluid actuators 24 associated with thelongitudinal member 12 and a pair of transverse fluid actuators 24 aassociated with the transverse member 14, 14 a. To rotate the cantileverfrom position M to position N, as shown in FIG. 6A, with the centre ofrotation at sliding/swivel assembly 20 a, the longitudinal fluidactuator(s) 24 associated with sliding/swivel assembly 20 c and/or 20 dis/are operated to push/pull separately or synchronously with thetransverse fluid actuators associated with sliding/swivel assemblies 20b, 20 c and 20 d being unlock (or free to extend/retract), or thetransverse fluid actuator(s) 24 a associated with sliding/swivelassembly 20 b and/or 20 c is/are operated to push/pull separately orsynchronously with the longitudinal fluid actuators 24 associated withsliding/swivel assemblies 20 b, 20 c and 20 d being unlocked (or free toextend/retract), or the longitudinal and transverse fluid actuators areoperated cooperatively. Unlocking a hydraulic cylinder includesactivating a solenoid to by-pass a motion-lock or brake valve, such as,a piloted check valve connected across the fluid lines of the fluidactuator.

In another example, as shown in FIG. 6B, the transverse fluid actuator24 a associated with the sliding/swivel assembly 20 a is operated incounter-motion with the transverse fluid actuator 24 a associated withthe sliding/swivel assembly 20 b to create a torque for rotating thecantilever 10 about a virtual centre of rotation lying within the foursliding/swivel assemblies 20. Alternatively, the pair of transversefluid actuators 24 a associated with transverse rail 14 a and the pairof transverse fluid actuators 24 a associated with transverse rail 14are similarly operated in counter-motion, as shown by the arrows in FIG.6B, to rotate the cantilever 10 from position M to position L. In asimilar manner, the longitudinal fluid actuator(s) 24 associated withone longitudinal member 12 is/are operated in counter-motion with thelongitudinal fluid actuator(s) 24 associated with the other longitudinalmember 12 to create a torque to rotate the cantilever 10. Alternatively,a combination of counter-motions or push/pull of both the transverse andlongitudinal fluid actuators in synchronous cooperation creates additivetorques to rotate the cantilever 10. In the present invention, rotationof the cantilever 10 involves rotation of each of the foursliding/swivel assemblies 20 a . . . 20 d.

FIG. 7 shows a plan view of the cantilever 10 system with the envelop100 showing the locus of the drilling point P. The envelop 100 iscreated by a combination of translations of the cantilever 10 on thelongitudinal 12 and transverse 14,14 a members and rotation of thecantilever about the four sliding/swivel assemblies 20. As can be seenfrom FIG. 7, the envelop 100 of the drilling point P according to thepresent invention is larger than that described by an envelop of aconventional cantilever, such as the rectangular envelop Q₁P₁P₁₁Q₂described in U.S. Pat. No. 6,717,027.

FIG. 8 illustrates rotation of the cantilever 10 system about the foursliding/swivel assemblies 20 without having to move the transverse rails14,14 a. In contrast, translation of the cantilever of U.S. Pat. No.7,083,004, as seen from FIG. 1, involves shifting the curved rails 444;such shifting of the curved rails 444 of U.S. Pat. No. 7,083,004 islaborious and time-consuming; in other words, translation of the curvedrails of U.S. Pat. No. 7,083,004 is inconvenient and entailsunproductive operation.

In the above embodiments, two or four fluid actuators 24, 24 a areassociated with each of the transverse and longitudinal members. Inanother embodiment, more than four fluid actuators are possible; one setof cylinders may be used on each of the two sides of thetransverse/longitudinal members, that is, the fluid actuators arearranged in parallel. In yet another embodiment, two sets of fluidactuators are arranged in series so that displacement (translation androtation) of the cantilever 10 can be operated continuously instead ofintermittently/stepwise manner.

While specific embodiments have been described and illustrated, it isunderstood that many changes, modifications, variations and combinationsthereof could be made to the present invention without departing fromthe scope of the invention. For example, the pin 28 on each rail block27 and the cooperating holes 29 on the transverse/longitudinal membermay be aligned vertically (in the Z-direction) instead of horizontally.In addition, the holes 29 need not be equally or uniformly spaced aparton the transverse/longitudinal member. In another example, eachlongitudinal/transverse member may be translated by means of rack andpinion instead of pin and holes on a rail block. In another example, ascrew actuator may be used instead of a fluid actuator. In yet anotherexample, other translation means such as sprocket-chain or pulley-beltsystem may be used instead of a fluid actuator. Further, the cantileversystem of the present invention can also be used on any oil drillingplatform having 3 or more legs, on a semi-submersible rig, and so on.

The invention claimed is:
 1. A drilling rig comprising: a platformhaving a pair of substantially parallel transverse members near an edgethereof; a cantilever mountable on the platform, said cantilever havinga pair of substantially longitudinal members along the length of thecantilever, said longitudinal members are substantially orthogonal tothe pair of transverse members; and a plurality of sliding and swivelassemblies connecting the longitudinal and transverse members at eachinterposition of said longitudinal and transverse members, wherein eachof the plurality of sliding and swivel assemblies comprises an uppersliding block, a lower sliding block and a swivel member interconnectingthe upper and lower sliding blocks, such that the sliding and swivelassemblies are moveable relatively on the relevant longitudinal ortransverse member to translate and/or rotate the cantilever with respectto the platform.
 2. A rig according to claim 1, wherein said uppersliding block is connected to the longitudinal member whilst the lowersliding block is connected to the transverse member.
 3. A rig accordingto claim 1, wherein the swivel member comprises shoulders, necks andannular surfaces to withstand torsion, tension and compression loads,with each pair of mating surfaces having a bearing plate therebetween.4. A rig according to claim 1, further comprising an actuator associatedwith each longitudinal member and transverse member.
 5. A rig accordingto claim 4, wherein the actuator comprises two or more pairs ofactuators.
 6. A rig according to claim 5, wherein the pair of actuatorsassociated with a sliding/swivel assembly are connected in series orparallel.
 7. A rig according to claim 4, wherein each of the pluralityof sliding and swivel assemblies is connected by said actuator to theassociated longitudinal member and/or transverse member via a railblock.
 8. A rig according to claim 4, wherein the actuator is a fluidactuator, a screw actuator or a rack/pinion assembly.
 9. A rig accordingto claim 1, wherein the pair of transverse members are unequal inlength, with said transverse member near the edge of the platform beinglonger.
 10. A method of displacing a cantilever on platform of adrilling rig, said method comprising: disposing said cantilever on saidplatform, with said cantilever having two substantially parallel membersalong the cantilever's longitudinal dimension; disposing twosubstantially parallel transverse members near an edge of said platform;interconnecting said longitudinal and transverse members by a pluralityof sliding and swivel assemblies at each interposition, wherein each ofthe plurality of sliding and swivel assemblies comprises an uppersliding block, a lower sliding block and a swivel member interconnectingthe upper and lower sliding blocks; and connecting an actuator betweeneach of the plurality of sliding and swivel assemblies and saidassociated longitudinal/transverse member, wherein said actuator is oractuators are operable to translate and/or rotate said cantilever withrespect to said platform.
 11. A method according to claim 10, whereineach said actuator comprises two or more actuators associated with eachof the longitudinal and transverse members.
 12. A method according toclaim 11, wherein two actuators associated with a sliding/swivelassembly are connected in series or parallel.
 13. A method according toclaim 10, wherein the actuator is a fluid actuator, screw actuator or arack/pinion assembly.
 14. A method according to claim 10, whereinrotation of the cantilever about one of the plurality of sliding andswivel assemblies is executed by actuating one or more actuatorsassociated with one or more of the other sliding and swivel assembliesto create a turning moment about said sliding/swivel assembly.
 15. Amethod according to claim 10, wherein rotation of the cantilever isexecuted by counter-motions of the actuators associated with therelevant longitudinal members or transverse members, or both members.16. A method according to claim 10, wherein each sliding and swivelassembly is connected by an actuator to the relevant longitudinal memberand/or transverse member by a rail block.
 17. A method according toclaim 16, wherein the rail block is engageable with holes on therelevant longitudinal and transverse members by a pin.
 18. A methodaccording to claim 12, wherein two actuators associated with eachsliding and swivel assembly are connected in series so that translationand rotation of the cantilever are operable continuously.
 19. A methodaccording to claim 10, wherein said upper sliding block is connected tothe longitudinal member whilst the lower sliding block is connected tothe transverse member.
 20. A method according to claim 19, wherein theswivel member comprises shoulders, necks and annular surfaces towithstand torsional, tension and compression loads, with each matingpair of surfaces having a bearing plate therebetween.